Telephone system



Jan. 6, 1942. .l. BAUMFALK ETAL TELEPHONE S YSTEM Filed July 5,

1940 4-Sheets-Sheet l ,/.BAUMFALK /NVENTOg 0 C. HALL ATTORNEY Jan. 6, 1942. L BAUMFALK ET AL 2,268,635 TELEPHONE SYSTEM Filed July 5, 1940 4 Sheets-Sheet 2 ATTORNEY Jan.6,1942 J. BAUMFALK HAL v 2,268,635-

TELEPHONE SYSTEM Fild July 5, 1940 4 sheets-sheet s J. BA UMR! LK /NL/wTo/es: 0. HALL ATTORNEY Patented Jan. 6, 1942 TELEPHONE SYSTEM J ohn Baumfalk, Clifton, and Oliver C. Hall, Radburn, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 5, 1940,'5seria1N0. 344,026 p 10 Claims.

This invention relates to telephone systems and particularly to systems comprising a local unattended automatic ofce, a tandem unattended automatic oiice and a master oice.

Objects of the invention are the provision of means for facilitating the completion of calls from subscribers in an unattended office through a tandem unattended oice to an operator in a master olce, a minimization of the operations required at calling stations for establishing such connections, and the provision of an ecient trunking arrangement between these oices.

A feature of the invention is a telephone system comprisingan unattended local office, an unattended tandem omce, trunks between said oliices, a trunk circuit for each of said trunks in the local ofice having two sets of conductors through which a calling line may be connected to the trunk, and an incoming group selector associated with each of these trunks in the tandem oice, each of the trunk circuits in the local oice being arranged to automatically control the operation of the associated incoming selector in the tandem o'ice to select a predetermined group of terminals in its bank responsive to seizure of the trunk circuit through one but not'the other of its two sets of conductors.` According 'to this feature the incoming selector associated in the tandem oilice with a trunk seized in the local omce is automatically operated to select a group of trunks leading to a master olce when a calling line is connected to the associated trunk circuit through one of two paths of access and is operated in response to dial impulses from the calling station when a calling line is connected thereto through the other of the two paths of access.

Another feature of the invention is a telephone system comprising local and tandem unattended ciices and an attended master oice and a trunk circuit in the local unattended cnice associated with a trunk to the tandem unattended olce, the trunk circuit having two sets of conductors through which it may be selected for use respon sive to the first digit dialed by a calling subscriber, and having means operatively responsive to seizure through one but not the other of these sets of conductors for transmitting a directive impulse over the trunk to the tandem oice without further dialing by the calling subscriber. According to this feature, the trunk circuit is connected to terminals in two different levels of the banks of local selectors, the dialing of the first digit of subscribers numbers on a call to a station in the tandem office effecting seizure of f the trunk circuit through one level of a selector and one of thertwo sets of conductors, and the dialing of another digit, for instance the digitO, on a ,call to an operator in the master o'ice, effecting seizure through another level and the other set of conductors. The impulse transmitted tothe tandem office eiects the selective operation of the incoming selector associated with the trunk to select a group of terminals connected to trunks between the tandem and master oices. y

Another feature of the invention is a telephone system comprising local and tandem unattended cices and an attended master office, the local unattended oflicecomprisingboth dial and manual stations, dial stations being connected to trunks to the tandem ofce responsive to the Vdialing of one digit, and manual stations being connected thereto responsive to removalof the receiver to originate a call, each of the trunk circuits associated with trunks to the tandem oice being connected through a first set of conductors to terminals in one level of local selectors for seizure on calls to subscribers in the tandem oilice, and through a second set of conductors to terminals in another level of these selectors for seizure on calls to an operator'in the master oiice, to terminals in the banks of line switches associated with manual stations, and to the alarm sender apparatus which is effective when a trouble condition exists in the local unattended ofce to originate an alarm call to the master cnice, the trunk circuit being provided with relay means responsive to seizure through the second set of conductors for automatically transmitting a selective impulse to the associated incoming selector in the tandem ofce to eiect selection of the group of trunks between the tandem and master oliices.

A cleai` and complete understanding of the in-` vention willbe facilitated by considering a telephone system in which the invention is embodied,

Vone such system being shown in the drawing which forms a part of this specication. The invention is not limited in its application to th-e particular system shown but is generally applicable to systems comprising local and tandem unattended offices and a master attended office. Referring to the drawings: f Fig. 1 shows, in an unattended local central oflice LO, a manual subscribers station M, line LI and line circuit LCI, an automatic subscribers station A, line L2 and line circuit L02, a subscribers station B, line L3 and line circuit'LC3, a line switch LS individual to the line LI, a line LFI, SI,

nder LFI having access to a group of lines including the line L2, a first selector SI associated with the line iinder LFI, an incoming selector ISI, miscellaneous alarm apparatus MA, and a ringing and tone circuit RC;

Fig. 2 shows a two-way trunk circuit TCI associated with a trunk TI2 between th'e unattended local central office LO and an unattended local and tandem central oflice TO, the trunk circuit TCI being connected to the incoming selector ISI of Fig. l and to terminals in the banks of selector SI and other similar selectors;

Fig. 3 shows, in the local and tandem ofIice TO, a two-way trunk circuit TC2 associated with trunk TI2; and

Fig.` 4 shows, in the local and unattended olce TO, an incoming selector IS2 associated with the trunk circuit TG2 of Fig. 3, subscribers stations X and Y, lines L4 and L5 and line circuits LC4 and L05, a line finder LF2, a rst selector S2, a connector C2, an incoming selector IS3, and -a two-way trunk circuit TG3 associated with the incoming selector IS2; Fig. 4 also shows a trunk T34 between the local and tandem unattended oice TO and a master cnice MO, and in the master oilice a two-way trunk circuit TC4 and jack J4 and a cord CD at an operators position.

The subscribers station M represents manual, common battery stations which are equipped with individual line switches for connecting the associated lines with trunks on originating calls. The stations A, X and Y represent common battery stations, each provided with a dial or other impulse sender for controlling the establishment of desired connections. eitlier .a manual station or a dial station. The lines LI, L2 and L4 are also connected to terminals in the banks of connector switches for receiving incoming calls; the line L3 is also connected to terminals in the banks linender` switches if it is a dial subscribers line or to a to the talking and test brushes I I, I2 and I3, the

line switch LS is provided with a brush I4 for giving a class-of-subscriber indication to the selected trunk.

The line-nder, selector and connector switches olce and LF2, S2, IS2, IS3 and C2 in the local and tandem unattended oilice are all of the twomotion step-by-step type. Each of the linender, selector and connector switches is represented in the drawing by a set of brushes and one, two or three sets of terminals, all of the magnets, relays and other associated apparatus being omitted. The three sets of terminals 35, 36 and 3'I of selector SI represent, respectively, a

level giving access to a group of connectors including the connector CI for completing local calls, a level corresponding to the rst digit of the subscribers numbers in` the local and tandem office and giving access to a group of trunks including trunk TI2, and a level, usually 0 level, r

giving access to the same group of trunks on calls to an operator in the master office. The three sets of terminals |54, |55 and |56 of selector` S2 represent, respectively, a level giving access to a group of connectors including the connector C2 The station B may be ISI and C I in the local unattended for completing local calls, a level corresponding to the vfirst digit of the subscribers numbers in the local oflice LO and giving access to the group of trunks including trunk TI2, and a level, usually 0 level, giving access to a group of trunks including trunk T34 on calls to an operator in the master oirlce. The two sets of terminals |34 and |35 of incoming selector IS2 represent, respectively, a level giving access to the group of trunks including trunk T34 and a level giving access to a group of connectors C2. The two sets of terminals |64 and |65 of incoming selector IS3 represent, respectively, a level giving access to the group of connectors C2, and a level giving access to the group of trunks including trunk TI2 for completing calls from the master oice to the local office LO. The selector switch has, in addition to the line and test brushes, a fourth brush through which the class of the calling subscriber connected thereto may be indicated to the selected trunk for use on calls to the master oilice. Reference may be had to the aforementioned 2nd edition of Automatic Telephony, pages 53 to 65, for a complete description of such switches when used as selectors and connectors. Reference may be had to the patent to R. L. Stokely No. 1,799,654, April 7, 1931, and the patent to T. L. Dimond, No. 2,210,068, granted Aug. 6, 1940, for a complete description of such switches whenV used as line finders and for a description of the line circuits of the lines connected to the banks of line-finder switches.

The miscellaneous alarm .apparatus includes an alarm sender for seizing an outgoing trunk and may be similar to that disclosed in the patent to J. N. Walters, No. 2,262,595, granted Nov. 1l, 1941.

The two-way trunk circuit TCI connects the associated trunk TI2 through conductors 5| and 52 to a set of terminals in the banks of each of a group of line switches LS, to a set of terminals in the 0 or other master office levelof each of the iirst selectors SI, and to the miscelleaneous alarm apparatus MA, connects the trunk TI2 through conductors 55 and 56 to a set of terminals in another level of each of the selectors SI, which level corresponds to the first digit of sub scribers numbers in the local and tandem oftice, and connects trunk TI2 through conductors 51 and 58 to the incoming selector ISI. The trunk circuit comprises a repeating coil RCI, relays for repeating dial impulses on outgoing calls, relays for repeating dial impulses on incoming calls,

'and supervisory and other control relays as hereinafter described in detail. It also includes means comprising a relay 14 for automatically causing the transmission of an impulse over trunk TI2 to advance the brushes of the associated incoming selector IS2 in oflice TO to select the rst level of its banks and a trunk therein, such as trunk T34, leading to the master office; and includes means comprising relays 1| and I2 for controlling the transmission of a class of subscriber signal to the answering operator on calls to the master oce.

The two-way trunk circuit TC2 connects the trunk TI2, through conductors |25 and |26, to the incoming selector IS2 and, through conductors I 2|, |22 and |23, to terminals in the banks of local selectors S2 and incoming selectors IS3. It comprises a repeating coil RC2, relays for repeating impulses on incoming calls, relays for repeating impulses on outgoing calls, and supervisory and other control relays as hereinafter described.

The two-way trunk circuit TO3 connects the trunk T34 to the incoming selector IS3 and. to sets of terminals in the banks of local selectors S2 and incoming selectors IS2 and comprises means for transmitting signals to, and receiving signals from, the master office. The two-way trunk circuit TC4 in the master oiiice c-onnects the trunk T34 to jacks Jaand comprises means for receiving seizure and supervisory signals from the cnice TO and for transmitting seizure, selective and supervisory signals to the cnice TO. The trunk circuits TG3 and TC4 may be similar to the trunk circuits TC3 and TC4 shown in detail in the patent to R. B. Buchanan et al., No. 2,233,282, granted Feb. 25, 1941.

Assume rst that a call is initiated at station A, Ithat the line L2 is connected through a line nder LFI to the associated rst selector SI and that the brushes of switch SI are advanced under control of the train of impulses created by the dialing of the first digit of the number of the station with which connection is desired to select the corresponding group of terminals, and that the brushes are thereupon automatically advanced in the selected group to select and seize the rst unguarded set of terminals. If the subscriber at station A is calling another station B in the same oiiice, the selector SI is operated in response to the impulses created by the dialing of the rst digit of the called subscribers nurnber to select a group of terminals, represented by the terminals 35, and is automatically operated to select an unguarded set of terminals therein. Upon selection of an unguarded set of terminals, for instance the terminals 35, the calling line is connected through brushes 3|, 32 and 33 to a connector CI having access to the called line; and the dialing of the last two digits of the called subscribers number elects the operation of the connector to select the set of terminals to which Ithe called line is connected.

If, however, the subscriber at station A is calling a subscriber in the local and tandem ofce TO, the selector SI is operated in response to the train of impulses created by the dialing of the first digit of the number of the called station to select the group of terminals represented by the terminal set 36, and is automatically operated to select an unguarded set of terminals therein. Upon Selection of an unguarded set of terminals, for instance the terminals 36, the calling line is ,connected through brushes 3|, 32, 33 and 34 and conductors 55, 58, 53 and 54 to the trunk circuit TCI. Upon engagement of the brushes of selector SI with terminals 3S, -a circuit is closed for operating relay 98 of trunk circuit TCI. This operating circuit is traced from battery through the lower winding of relay 9U, inner lower back contact of relay 15, lower left winding of repeating coil RCI, outer lower back contact of relay 15, inner lower back Contact of relay 13, conductor 56, terminal and brush 32 of selector S! brush `22 and terminal line nder LFI, through one conductor of line L2 and the station A, back through the other conductor of line L2, terminal and brush 2| of line nder LFI, brush 3| and terminal of selector SI, conductor 55, inner upper back contact of relay 'i3 outer upper back contact of relay 15, upper left winding of repeating coil RCI, inner upper back contact of relay 'I5 and through the upper winding of relay 9E) to ground. Relay 8|] closes a circuit for operating the slow-to-release relay 81. Relay B'I closes a circuit for operating the slow-to-release relay 86, closes a circuit for operating relay 82, and connects ground, through conductor 53, to the terminal engaged by test brush 33 of selector SI to hold this selector and the line nder LFI in usual manner and to prevent selection of trunk circuit TCI by ano-ther selector or by a line switch or by the miscellaneous alarm apparatus MA. Relay 88 also connects ground to conductor 53 and closes the operating circuit for relay 82. Relay 82 disconnects the windings of relay 85 from the conductors of trunk T|2 and closes a circuit over trunk TIZ for operating relay |06 of trunk circuit TC2. This circuit is traced from battery through the lower winding of relay |05, inner lower back contact of relay I I0, lower left winding of repeating coil RC2, outer lower back contact of relay I I El, lower back contact of relay |0I,

lower conductor of trunk TI2, upper back contact of relay 9|, upper front contact of relay 98, inner upper back contact of relay 83, upper front contact of relay 82, upper right winding of repeating coil RCI, upper front contact of the normally operated relay 88, upper winding of polarized relay 84, outer lower back contact of relay 83, inner lower front contact of relay 82, lower right winding of repeating coil RCI, outer lower front contact of relay 82, inner lower back. contact of relay 83, inner lower front contact of relay 98, inner lower back contact of relay 9|, upper conductor of trunk TI 2, upper back contact of relay IDI, outer upper back contact of relay |I0. upper left winding of repeating coil RC2, inner upper back contact of relay IIU, and through the upper winding of relay |86 to ground. Relay |06 closes a circuit for operating slow-to-release relay |03, connects ground to conductor |23 to prevent seizure of trunlr. circuit TC2 by a local selector S2 or an incoming selector IS3, and

bridges condenser |I5 across the inner ends of the right windings of repeating coil RC2. Relay |03 closes a circuit, including ythe upper back contact of relay 84, for operating relay I I3. Relay ||3 also connects ground to conductor |23, disconnects the right windings of repeating coil RC2 from conductors I2I and |22, and closes a bridge across conductors |25 and |28 leading to the incoming selector ISZ. This bridge may be traced from conductor |25 through the outer up- Vper front contact of relay |I3, upper right winding of repeating coil RC2, inner upper front contact of relay I I3, lower winding of polarized relay III, outer lower front contact of relay |06, lower right winding of repeating coil RC2, middle lower front con-tact of relay II3 to conductor |26. The line relay (not shown) of selector ISZ is thereby operated to prepare for selective operation of this switch responsive to dial impulses from the calling station A. When the subscriber at station A dials the next digitl of the called subscribers number, relay 9|) releases and reoperates in response to each impulse of the train, thereby repeating these impulses through its inner front contacts to the incoming line relay |06 of trunk circuit TC2. Relay |86 in turn repeats these lmpulses at its outer lower front contact to the line relay of incoming selector ISZ. When relay 9U releases in response to the first impulse of the train, it closes a circuit from ground through its lowerback contact, the outer upper front contact of relay 81, outer lower back contact of relay 89 and the outer upper back contact of relay 13, for operating slow-to-release` relay 83. Relay 83 disconnects the bridge comprising the right.

relay I 06 of trunk circuit TG2 after each impulse. At its inner lower front contact, relay 83 connects battery to the upper conductor of trunk TI2 to energize the upper winding of relay |06; and, at its upper front contact, relay 83 connects 'ground to thel lower conductor of trunk TI2 to energize the lower winding of relay |06. The release of relay |06 in response to the iirst impulse of the train closes a circuit, through its back contact and the upper front Contact of relay |03, for operating slow-to-release relay I I2. Relay II2 short-circuits the right windings of repeating coil RC2 to insure the reolperation of the line relay of selector IS2 after each impulse. Relays 81 and 86 of trunk circuit TCI and'relay |03 of trunk circuit TC2 are slow in releasing and remain operated during the response of relays 90 and |06 to dial impulses. Relay 83 of trunk circuit TCI and relay |I2 of trunk circuit TCZ are also slow in releasing and remain operated until after the last impulse of the train has been received by relays 90 and |06, respectively. The

vselector IS2 is operated in response to this train the conductors of trunk TI2 to hold relay |06 operated, resistance 92 being momentarily connected in parallel with the upper winding of relay 84 during the continuity action of the springs of relay 83 to prevent operation of relay 84. The release of relay II2 reconnects the lower winding of relay III in series with the right windings of repeating coil RC2 across conductors |25 and |26 to hold the line relay of selector IS2 operated. After completion of group selection the brushes I3I, |32 and |33 of selector IS2 are advanced in usual manner to select an unguarded set of terminals in the selected level.

Assume first that the selector IS2 is operated to seize the set of terminals |35 connected to a connector switch C2 having access to the called line L5 in oice TO. A circuit is thereupon closed through the brushes |3| and |32 of seshown) of the seized connector; and this relay is controlled by the impulses created by the dialing of the last two digits of the called subscribers number to select the called line. A test of this line is made to determine whether it is idle or busy and, if idle, ringing current is connected to the line in usual manner. When the call is answered at the called station Y, the connector reverses the current in the circuit through the 255 brushes I3I and |32 of selector IS2, conductors |25 and |26 and the lower winding of relay I| of trunk circuit TC2 to cause the operation of this relay. Relay I|I closes a circuit for operating relay I 0I. Relay IOI interchanges the connections between the windings of relay |06 and the conductors of trunk TI2 so as to reverse the current through these conductors and thereby cause the operative energization of the upper winding of polarized relay 84. Relay I0| also closes a circuit for holding relay |03 and closes a short circuit around the upper, high resistance Winding of relay |I|. Relay 84 closes a circuit for operating relay 13. Relay 13 interchanges the connections between the windings of relay 90 and conductors 55 and 56, thereby reversing the current through these conductors to effect any desired supervisory operation, such, for instance, as charging for the call. Relay 13 also tacts of relay 90 and causes the release of relay 12 as hereinafter described on a call to the master oiiice; but the closing of these circuits and the release of relay 12 are of no utility on a call from station A to station Y. The talking connection includes the windings of repeating coils RCI and RC2 and is under the control of the calling subscriber. If the called subscriber replaces the receiver before the connection is released, the connector effects a reversal of current through conductors |25 and |26 and the lower winding of relay III to cause the release of this relay. The release of relay III causes the release of relay I0| and the release of relay IDI reverses the current through the conductors of trunk TI2 to release relay 84. The release of relay 84 causes the release of relay 13, thereby reversing the current through conductors and 56. When the connection is released by the calling subscriber, relay 90 r'eleases, causing the successive release of relays 81 and 86. With both of relays 81 and 86 released, the holding and guarding ground potential is disconnected from conductor 53 to cause the release of the selector SI and line finder LFI, these switchesbeing restored to normal in usual manner. The release of both of relays 81 and 86 also causes the release of relay 82, thereby reconnecting the windings of relay 85 through the right windings of repeating coil RCI to the conductors of trunk TI2. The aforementioned re- -lease of relay opens the bridge across the lector IS2 for operating the line relay (not conductors of trunk TI2 to effect the release of the line relay |06 of trunk circuit TG2. The release of relay |06 causes the successive release of relays |03 and I I3, thereby opening the bridge across conductors |25 and |26 to cause the release of the line relay of the connector C2 and thereby effect the restoration of this switch and the incoming selector IS2 to normal in usual manner.

If now the subscriber at station A originates a call to the master oiiice, the selector SI is operated in response to the dialing of the first digit, for instance 0, to select the group of terminals represented by the terminal set 31, and is automatically operated to select an unguarded set of terminals therein. Upon selection of a set of terminals, for instance the set 31, the calling line is connected through brushes 3|, 32, 33 and 34 and conductors 5I, 52, 53 and 54 to the trunk circuit TCI. Relays 14 and 90 are thereupon operated in a circuit which includes conductors 5I and 52, brushes 3| and 32 of selector SI, brushes 2| and 22 of line nder LFI, and the calling line L2. Relay 1I may or may not be operated depending upon the class of service to which the subscriber at station A subscribes. The operation of relay 90 causes the successive operation of relays 81, 86 and 82 of trunk circuit TCI and the successive operation of relays |06, |03 and |I3 of trunk circuit TCE as hereinbefore described. Relay 14 connects groundrto conductor 53 and opens the normally closed energizing circuit of relay 88, thereby causing the release of relay 88. Relay 88 is slow in releasing so as to maintain the bridge across the conductors of TI2 for a long enough time to insure the operation of relay |06 of trunk circuit TC2 and the operation of the line relay of the incoming selector IS2. When relay 88 releases, it opens the bridge across the conductors of trunk TI2 to cause the successive release of relay I 06 of trunk circuit TG2 and the line relay of the incloses short circuits around the inner front con- "75 coming selector IS2. The release of relay 88 also causes the operation of slow-to-operate relay 89. Relay 89 short-circuits the winding of relay 1,4 to cause its release and recloses the bridge across the conductors of trunk TI2 to reoperate relay |06 of trunk circuit TG2 and the line relay of the incoming selector ISZ. In this manner relays 14, 88 and 89 function to transmit an impulse over trunk T|2 to cause the incoming selector IS2 to be stepped up to the first level of its bank without further dialing on the part of the calling subscriber. 'Ihe selector IS2 thereupon hunts Vfor and seizes an unguarded set of terminals, such as the terminals I34 connected to a trunk circuit TG3 and trunk T34 leading to the master oiice MO. The trunk circuit TC4 in the master oflice is thereby operated to light an answering lamp AL and when the call is answered by insertion of the plug of the cord CD in jack J4, the lamp AL is extinguished and the trunk circuit TG3 operates to reverse the current through the brushes I3I and |32 of selector IS2, conductors |25 and |25 and the lower winding of polarized relay ||I. Relay I II operates closing the circuit for operating relay IBI. through the conductors of trunk T|2 to operate relay 84 of trunk circuit TGI. Relay 84 closes a circuit for operating relay 'I3 but relay 'I3 is ineffective to reverse the current through conductors 5| and 52 and the calling subscribers line. Relay 13 closes a circuit including condenser 'I0 and the one or the other of conductors 68 and S9 for transmitting a class-of-calling station indication to the answering operator, the tone signal being terminated by the release of relay '12. Relay I3 also closes short circuits around the inner lower front contacts of relay 90 and closes a circuit including the back contact of relay I4 and a front contact of relay 89 for holding relay 8l operated to maintain the connection of holding ground to conductor 53.

The talking connection includes the repeating coils RCI and RC2' and is under the joint control of the calling subscriber and the answering Operator. If the calling subscriber replaces the receiver before the operator disconnects, relay 90 releases but relays 84, 13, 8l, 88 and 82 are held operated and the selector SI and line nder LFI cannot restore to normal. The release of relay 90 inserts the high resistance lower winding of relay 84 in the bridge across trunk T|2 causing the release of relay |06; but relay III is held Relay HH reverses the current interval, the miscellaneous alarmapparatus 'MA operates in the manner described in the aforementioned patent to J. N. Walters to seize trunk circuit TCI and trunk T|2 leading to oiiice LO, relays "I4, 88 and 89 being operated to automatically control the operation of the incoming selector IS2 to extend the connection over a trunk T34 to the master oice. When the call is answered, relay III of trunk circuits TG2 and relays 84 and -13 of trunk circuit TCI are operated in succession. Relay 'I3 connects ground to conductor 50 to cause the transmission of a tone from the miscellaneous alarm circuit MA to the answering operator in the master oflice to indicate the character of the trouble. I

If the subscriber at station X in the office TO originates -a call, a line nder LF2 is operated to connect the line L4 to a first selector S2. The selector is controlled by the impulsescreated by the dialing of the first digit of the called subscribers number to select a corresponding group and an unguarded set of terminals therein. If

the 'called subscriber is in the same ofce, the selected set of terminals connects to a connector switch G2 having access tothe called line; and the connection is completed by the dialing of the remaining digits of the called number in the usual manner.4 If the selector S2 selects a group and a set lof terminals therein leading to a trunk` circuit TG3 associated with a trunk T34` leading to the master voi'iceMO, the call is completed as described in the aforementioned f patent to Buchanan et al. v

Ifon a call lfrom station X, the selector S2 is operated to select a group and a set of terminals therein connected to a trunk circuit TG2 associated with a trunk TI2 leading to the oice LO, the line relay |02 of trunk circuit TG2 is operated by the currentin a circuitfrom battery through its lower winding, inner lower back contact'of relay I| 3, lower right winding of repeating coil operated by its two windings in series through the inner upper front contact of relay IOI, the resistance of the upper winding of relay III being high enough to cause the release of the line relay in the trunk circuit TG3 and thereby transmit a supervisory signal tothe master office. When the operator disconnects, the reversal of current over trunk T34 causes the successive release of relays III, I0|, 84 and 13. The release ofthe connection by the calling subscriber, after the operator has disconnected, causes the successive release of relays 90, 8l, 85 and 82 in trunk circuit TCI, and the successive release of relays |06, |03 and II3 in trunk circuit TG2. The release of relay 87 causes the release of relay 89; and relay 89 closes the circuit for operating relay 88. When the connection is released by both the calling subscriber and the operator, the trunk circuits, TC| TG2, TG3 and TG4 are normal andthe selectors Si and IS2 and the line nder LFI are all restored to normal in usual and well-known manner. If the subscriber at the'manual station M initiates a call, the line switch LS is controlled RC2, outer lower back contact of relay II3, inner lower back contact of relay II4, conductor |22,

terminal and brush |52 of selector S2, brush |42'l of the line finder LF2, through one of the conductors of line L4 and the telephone at station X, back through the other conductor of line L4, terminal and brush |4| of line finder LF2, brush I5-I and terminal of selector S2, conductor 2|, upper back contact of relay I I4, outer upper back contact of relay II3, upper right winding of Vrepeating coil RC2, inner upper back contact of relay I I3 and through the upper winding of relay |02 to ground. Relay |02 closes a circuitfor operating slow-to-release relay |04. Relay |04 closes a circuit for operating,slow-to-release relay |05, opens a point in the operating circuit of relay |I3 to prevent the operation of this relay in case the trunk T|2 is seized in the local office LO before it is marked busyin-this oiiice due to seizure in oice TO, closesacircuit for operating relay |10, and closes a circuit for energizingthe lower polarizingwinding of relay k| I4. Relay |05 connects condenser |I5 across the right ywindings of repeating coil RC2, closes a holding circuit for relay I I 0, closes a circuitH for maintaining the energization of the lower windingof relay II4,

and connects ground through conductor |23 to thek terminal engaged by the test brush |53 of selector S2 to hold the selector S2 and the line nder LF2 in the usual and well-known manner. Relay IIO disconnects the windings of relay |06 rfrom the windings of repeating coil RC2 and closes a bridge across the conductors of trunk TI2,fto cause the operation of incoming line relay 85 of trunk circuit TCI. This bridge includes 'the upper Winding of relay IIIII, the left windings Vof repeating coil RC2, back contacts of relay |01, front contacts of relay |02, and back contacts of relay IOI. Relay 85 connects ground to conductor 53 to guard against seizure of trunk circuit TCI- by a selector or line switch or by the miscellaneous .alarm apparatus in the local ofce LO. Relay 85 also closes a circuit for operating slow-to-release relay 16. Relay 18 closes the lcircuit -for energizing the loWerbiasing winding of relay 9| and closes a circuit for operating re- K '16, lower back contact of relay 8|, back contact of relay 18 to conductor 58. The'operation of the line relay of selector ISI prepares the selector for response to dial impulses in the usual manner. When the subscriber at station X dials the next digit of the called subscribers number, vrelay |82 is alternately released and reoperated b'y each impulse of the train.` The release of relay |02 in response to the first impulse opens the bridge across the conductors of trunk TI2, to release -relay 85 of trunk circuit TCI, and closes a circuit through the middle lower front contact of relay |04 and outer lower back contact of relay |I4 for operating relay |01. Relay |01 disconnects the left windings of repeating coil RC2 from the contacts of relay |02 and connects battery and ground to these contacts so that when relay |02 reoperates at the end of the first impulsa-the line relay 85 of trunk circuit TCI is reoperated by the energization of its windings in separate grounded circuits over the conductors of trunk TI2, thereby insuring the reoperation of this relay at the end of each impulse.

Y Relays 11, 18, 19 and 80 constitute an impulse correcting repeater, controlled by relay 85 for transmitting corrected dial impulses tothe line relays of` incoming selector ISI and succeeding switches through which connection with the called line is established. The release of relay 85, closes a circuit through the outer upper front contact of relay and a back contact of relay 19 for operating relay 80. Relay 80 is fast in operating and slow in releasing. Relay 80 locks under control of relay 19, closes a circuit including the lower back Contact of relay 8| for operating slow-to-release relay 11, closes la circuit for operating slow-to-release relay 8| and closes a circuit for operating relay 19. Relay 11 closes a bridge across conductors 51 and 58 which eX- cludes the` windingsof repeating coil RCI to insure the reoperation of the line relay of selector VISI between dial impulses. VRelay 11 remains operated during Athe repeating of each trained impulses. Relay 8| opens the energizing circuit for the lower winding of relay 9| and closes a circuit for holding relay 11. Relay 19 opens the operating circuit of relay and connects its winding in series with the winding of relay 18. When relay 80 releases, it opens the bridge across conductors 51 and 58. thereby transmitting an impulse to the line relay of selector IS2. If relay has not reoperated before relay 80 releases, relay 19 is held operated and relay 18 is operated by the current in a circuit including the windings of these relays in series. When relay 85 reoperates at the end of the impulse, relays 18 and 19 release. The release of relay 18 closes the bridge across conductors 51 and 58 to reoperate the line relay of selector ISI. Relay 8| is slow in releasing and if the frequency of the dial impulses is high enough, for instance ten or eleven impulses per second, Arelay 8| remains operated while the train of impulses is being received and repeated to the selector ISI. In this case the bridge across conductors 51 and 58 is opened each time relay 80 releases and closed when relay 18 releases, Each succeeding release of relay 85 causes the reoperation of relays 80, 19 and 18 to repeat the impulses to the line relay of selector ISI and thereby advances the brushes 6|, 62 and 63 to the level corresponding to the digit dialed. If the impulses are being transmitted at a low rate, for instance eight or nine impulses per second, relay 8| releases before the next impulse causes the reoperation of relay 80; in which case the bridge across conductors 51 and 58 is closed at the back contact of relay 8| to end each impulse, relay 85 having reoperated to release relays 18 and 19 before relay 8| releases. The incoming selector ISI is automatically operated to select an unguarded set of terminals in the selected group, the selected set of terminals being connected to a connector switch CI having access to the called line.

The impulses created by the dialing of the last two digits of the called subscribers number by the subscriber at station X causes the operation of relays |02 and |01 of trunk TC2. Relays 85, 11, 18,719, 80 and 8| of trunk circuitv 'ICI operate as hereinbefore described to repeat these impulses through conductors 51 and 58, and brushes 6I and 62 of selector ISI, to connector CI to effect the selection of the called line in the usual manner. The connector CI makes the usual busy testand if the line is idle connects a ringing current source to the line to signal the called station.- When the call is answered connector CI functions in the usual manner to reverse the current through conductors 51 and 58 to operatively energize the upper winding of relay 9|. Relay 9| interchanges the connections ,between the windings of relay 85 and the conductors of trunk TI2, thereby reversing the current through these conductors to operatively energize the upper winding of relay I I4. Relay II4 interchanges the connections between the windings of relay |02 vand conductorsV I2I and |22, thereby reversing the current through these conductors to perform any desired supervisory operation, such for instance as charging for the call. The talking connection includes repeating coils RC2 and RCI and is under the control of the calling station. When the called subscriber replaces the receiver the connector again reverses the current through conductors51 and 58 to cause the release of relay 9I. Relay 9| reverses the current through the conductors of trunk TI2 to cause the release of relay I I4; and relay I|4 reverses the current over the conductors |2| and |22. When the callvthe connection in usual manner.

ing subscriber at station X replaces the receiver to release the connection, relay |62 releases causing the successive release of relays |04, and H0 and the disconnection of the guarding potential from conductor |23. The release of relay |ll2 opens the bridge across the conductors of T |2 to release relay 85 of trunk circuit TC|. The release of relay 85 causes the successive release of relays 'I6 and I5. Since relay 85 does not reoperate, relay 'I8 is operated in series with relay 'I9 to hold open the bridge across conductors 51 and 58 so as to cause the release of the line relay in the connector switch Cl, the connector Cl and selector ISI being thereby restored to normal in the usual and well-known manner.

The operator in the master oilce may call a subscriber in office TO or a subscriber in oiiice LO. In either case the trunk circuits T04 and TCS operate as described in the aforementioned patent to R. B. Buchanan et al. to repeat dial impulses. The rst train created by the dialing of the called subscribers number operates the associated incoming selector ISS to select a corresponding group and an unguarded set of terminals therein-` On a call to a station Y in ofoe TO, the succeeding trains of dial impulses effect the operation of a connector switch C2 to complete On a call to a station B in office LO, the terminals selecte-d by switch IS3 are connected to a trunk circuit TG2 and the succeeding train of impulses are repeated by trunk circuits T04, TG3, TG2 and TC| to operate the associated incoming selector IS! and a connector C| in oioe LO to complete the connection with line L3. trunk circuits TC2 and TC| on such a call is similar to that hereinbefore described on a call from station X in oice TO to station B in ofiice LO.

In the above-described system, the trunks between the tandem and master offices are connected to terminals in the ilrst level of incoming selectors IS2 associated with trunks from the local office, and each of the trunk circuits TC|. in the local ofice are arranged to automatically transmit a single impulse to the associated incoming selector in the tandem oflice on calls from the local to the master oflice. The trunks between the tandem and master ofces may, however, be connected to any desired level of these incoming selectors in the tandem oiiice, each of the associated trunk circuits in the local odos being arranged to automatically transmit as many impulses, on calls to the master office, as are needed to directively control the incoming selector to select the level in which the trunks to the master office are connected.

Although the trunk circuits TC| and TG2 are arranged for direct current, loop signaling, the invention is applicable to trunk circuits arranged for any type of signaling, for instance composite, simplex, or alternating current signaling.

What is claimed is:

l. In a telephone system, a first central o'ice, a second central oflice, a trunk between said ofces, two paths of access to said trunk in said first oflice, an incoming group selector connected to said trunk in said second oflice, subscribers lines in said oflices, subscriber controlled means in said iirst oilice for seizing said trunk through either one of said paths of access as desired, and means associated with said trunk and operative only if said trunk is seized over a certain one of the two paths of access for automatically operating said incoming selector to select a predetermined one of the groups to which it has access.

The operation of 2. In a telephone system, a rst' central cnice, a second central office, a group of trunks between said oiiices, subscribers lines in said offices, subscriber controlled group selector switches in said first oice for establishing connections between calling lines Vand called lines or trunks, means for connecting a calling line to a selector switch, two paths of access to each of the trunks of said group, one path of access comprising terminals in one group in the banks of said group selectors, the other path of access comprising terminals in a different group in the banks of said group selectors, incoming group selectors in said second office one for each of said trunks, and means in said rst office for each of said trunks effective upon seizure of the associated trunk through one but not the other of said paths of access for automatically causing the selective operation of the associated incoming selector in the second ofce to select a predetermined one of the groups to which it has access. y

3. In a telephone system, a rst central office, a second central oiice, a trunk between saidofces, two paths of access to said trunk in said irst oiiice, an impulse controlled incoming group selector connected to said trunk in said second oice, subscribers lines in said ofiices, subscriber controlled means in said rst ofce for seizing said trunk through either one of said paths of access as desired, and means associated with said trunk for automatically transmitting an impulse over said trunk upon seizure of said trunk through one but not through the other of said two paths of access for operating said selector to select a set of terminals in the first group of its bank.

4. In a telephone system, a rst oflice, a second oflice, subscribers lines in each of said oices, trunks between said offices, impulse controlled group selectors in said rst oice, impulse controlled incoming group selectors in said second office, each of said trunks being connected to terminals in two different groups in the banks of said group selectors in said first oiiice and to an incoming selector in said second oftice, a third ofce and an operators position therein, trunks between said second oice and said position, the last mentioned trunks being connected to a group of terminals in the bank of each of said incoming group selectors in the second oiiice, means responsive to the origination of a call at a subscribers station in said rst oflice for connecting thecalling line to one of said group selectors in the rst oiice, means including an impulse sender at the calling station for operating said one group selector to select one of said two groups on a call to a subscriber in said second ofce and to select the other of said two groups on a call to the operator in the third oflice and, to select a set of terminals in the selected group, the selected terminals being connected to an idle one of said trunks between said rst and second oices, and individual means for each of said trunks between the first and second officesresponsive to the selection of` the trunk in one oi said two levels of the bank of a group selector in said iirst ofce but not to the selection of said trunk in the other of said two levels for transmitting an impulse over the trunk to the associated incoming selector in the second oiiice to operate the selector to select the group of terminals to which are connected the trunks between said second ofce and said operators position withoutfurther operation of the impulsek sender at the calling station.

5. In a telephone system, a local unattended office, a local and tandem unattended oilice, a master office, subscribers lines in each of said unattended ofiices, an operators position in the master office, rst selectors in said local unattended ofiice and means for connecting a calling line to a rst selector, combined interlocal and master office trunks between said unattended ofcesLsaid combined interlocal and master ofce trunks being connected to terminals in one level of said selectors for use on calls to subscribers in said local and tandem oii'ice and to terminals in another level of said selectors for use on calls to an operator in the master oice, subscriber controlled means for operating a selector connected to a calling line to seize an idle one of said combined interlocal and master oice trunks through either of the levels to which said trunks are connected, incoming selectors terminating said combined interlocal and master office trunks in said local and tandem oice, first selec-tors in said local and tandem office, master office trunks between said local and tandem unattended office and said operators position, said master office trunks being connected to the first level of said incoming selectors and to a level of the first selectors in the local .and tandem ofce, and means associated with each of said combined interlocal and master oflice trunks in said local unattended oice elTective only upon seizure of the trunk through the level used for calls to the master office for automatically causing the operation of the associated incoming selector in the local and tandem oii'ice to select said group of master of fice trunks and an idle trunk therein.

6. In a telephone system, a first unattended office, a second unattended oiice, subscribers lines in each of said oices, impulse controlled selector switches for establishing connections between calling and called lines, trunks between said oiices, each of said trunks being connected to two levels in the banks of selectors in said first oiice and to an impulse controlled incoming selector in said second office, an operators position, trunks to said position connected to a group of terminals in the bank of each of said incoming selectors in the second oice, means responsive to the origination of a cali at a subscribers station in said first oice for connecting the calling line to a selector having access to the trunks to the second oiice and having access to other switches 'in the first office, means including an impulse sender at the calling station for operating the connected selector to seize an idle one of said trunks through either of said levels, as desired, or to seize another selector switch through which connection with a called line in the first oice may be established, individual means in the first oice foreach of said trunks automatically effective responsive to selection of the trunk through one but not the other of said levels of a selector in the first oflice to directively control the operation of the associated incoming selector inthe second oiTice to select the group of terminals to which are connected the trunks to the operator, and individual means associated with each of said trunks in said first oiiice for repeating dial impulses from the calling station to operate the associated incoming selector in the second olice to select another switch through which connection with a called line in the second ofce may be established.

7. In a telephone system, a iirst unattended cnice, a second unattended cnice, subscribers lines in each of said offices, two-way trunks between said offices, an operators position, trunks from said second office to said position, impulse controlled switches including local and incoming selector switches in each of said ofdces for establishing connectionsA between calling lines and called lines or between calling lines and said position, each of said two-way trunks being connected to an incoming selector in the second ofce to terminals in a level of local selectors in said second otlice and to terminals in two different levels of the banks of selectors in the rst oice, means including means responsive to the origination of a call for connecting the calling line to a local selector, means including an impulse sender at the calling station for operating the connected selector to extend the connection to another selector in the same office on a call to another line therein or to extend the connection through an idle one of said two-way trunks to the associated incoming selector in the other of said iirst or second offices, means for each of said trunks in the second office for repeating impulses to the associated incoming selector in the first omce to effect the completion of a connection with a called line in the iirst office, means for each of said trunks in the first cnice for repeating impulses to the associated incoming selectors in the second oflice to effect the completion of a connection with a called line in the second oice, and means for each of said trunks in the rst oiiice automatically effective in response to selection of the trunk through one but not the other of the two levels to which it is connected in the banks of the local selectors in the rst office to control the operation of the associated incoming selector in the second office to select the group of trunks leading to said operators position.

8. In a telephone system, a first unattended oflice, a second unattended ofiice, subscribers lines in each of said offices, some of the stations in said rst office being dial stations and others being manual stations, impulse controlled selector switches for completing desired connections, trunks between said oices, each of said trunks being connected to an incoming selector in said second oiice and to terminals in two levels of the banks of selectors in said first office, means responsive to the origination of a call at a manual station for connecting the calling line to one of said trunks, means responsive to the origination of a call at a dial station in said rst office for connecting the calling line to a selector in said first office, an operators position, trunks to said position connected to the terminals in one of the terminal groups in the banks of the incoming selectors in said second oice, individual means in the first office for each of said trunks between the first and second offices for repeating dial impulses from a connected calling dial station to control the group selecting operation of the associated incoming selector in the second office, individual means in the first office for each of said trunks between the rst and second oifices automatically eiiective in response to the connection of a manual subscribers line to the trunk or in response to the connection of a dial subscribers line to the trunk through the terminals in one but not through the terminals in the other of the two levels of a selector in the rst oiice to directively control the group selecting operation of the associated incoming selector in the second oilice to select said group of trunks to said operators position.

.9. In a telephone system, a rst oice, a second oice, subscribers lines and dial stations in said first oiiice, selector switches in said first oice, means for connecting each calling line to an idle one of said switches, trunks between said ofces, said trunks connected to terminals in two different levels of said switches, said switches operatively responsive to the dialing of a rst digit at a connected dial station to select the one or the other of said levels according to the digit dialed and to select an idle one of said trunks, other means in said rst oice for seizing an idle one of said trunks, incoming selectors in said second ofce, each of said incoming selectors connected to one of said trunks, an operators position, a group of trunks connecting said position to one of the levels of each of said incoming selectors, and means responsive to seizure of a trunk between said first and second oices through one but not the other of the levels of one of said selector switches or by said other means for selectively operating the associated incoming selector to select an idle trunk in said groups of trunks to said operators position.

10. In a telephone system, according to claim 9, means associated with each of said trunks in said first office effective upon seizure by one of said selector switches through said other level for repeating the impulses created by the dialing of a second digit at a connected dial station to selectively operate said incoming selector in said second oice.

JOHN BAUMFALK. OLIVER C. HALL. 

